Adjustable precision resistors



Dec. 15, 1964 J. P. SMITH, JR 3,161,348

ADJUSTABLE PRECISION RESISTORS Filed Sept. 24, 1965 2 Sheets-Sheet l INVENTOR.

John P. Smith ATTORNEY Dec. 15, 1964 Filed Sept. 24, 1963 J. P. SMITH, JR

ADJUSTABLE PRECISION RESISTORS 2 Sheets-Sheet 2 INVENTOR.

P. S "rh John m5 ATTORNEY United States Patent 3,161,848 ADJUSTABLE PRECISION RESISTORS John P. Smith, Jr., Allentown, Pa, assignor, by mesne assignments, to Nytronics, Inc., Phillipsburg, N.J., a corporation of New Jersey Filed Sept. 24, 1963, Ser. No. 311,074 2 Claims. (Cl. 338130) This invention relates to adjustable precision resistors, and is particularly directed to a form and construction of a variable resistor, that will permit such resistor to be made in small sizes and dimensions, with means for achieving a high degree of precision in the adjustment of the resistor, for use in a related external circuit.

In one form of conventional adjustable resistor, the adjustable value is derived through a movable tap which serves as an adjustable electrode or terminal, and which is arranged to be connected to an external circuit. Such use of the adjustable tap as one electrode or terminal of the resistor has certain disadvantages. Since external connections to an external circuit must be made to fixed terminals on the resistor structure, an additional resistance element must be connected between the movable tap and'one of the fixed terminals, in order to permit the tap to have full free movement over the entire dimension of the main resistance element as the tap seeks a desired point of adjustment on that resistance element. Such an auxiliary connection between the tap and one fixed terminal introduces a minimum fixed resistance which is always present in the total resistance value, and therefore represents the minimum value which can be achieved in the variable resistor. If such minimum value is to be diminished, then the dimension of that auxiliary element must be increased in cross section, which introduces a new problem in providing an element of maximum flexibility, that will not introduce a tensioning force on the movable tap electrode of the resistor.

A primary object of the present invention therefore is to provide an adjustable resistor in which the resistance elements are disposed as linear elements, thereby permit ting the adjustable element to move progressively over the entire linear element, and thereby enabling the resistance adjustment to be continuously variable, as distinguished from the helix type of resistor which is incrementally variable.

Another object of the invention is to provide an adjustable resistor in which two linear wire elements are disposed in parallel relationship with a bridging element movable along the two wires to include a selected length of the two wires in series to provide the adjustable resistance value desired, with the free ends of the two wires serving as fixed terminals for connection to an external circuit.

A further object of the invention is to provide an adjustable resistor of the foregoing type in which the bridging element is arranged to be moved along the two parallel wires by means of a micrometer device which permits extremely fine adjustable positioning of the bridging element to be achieved in order to establish very fine adjustment of the resistance Value included in the two wires and the bridging element for connection to an external circuit.

Another object of the invention is to provide a bridging element of efficient form and construction for establishing low resistance contact with each of the two wires While at the same time the bridging element is constructed to move freely along the two wires to a selected adjusted position to establish a desired resistance value in the circuit including the two wires and the bridging element, for connection to an external circuit.

The construction of the adjustable resistor of this invention, and the manner in which it operates, are described in the following specification, taken in connection with the accompanying drawings, in which FIGURE -1 is a schematic functional mechanical diagram showing the general arrangement of the elements that enter into the construction and operation of the adjustable resistor;

FIGURE 2 is a longitudinal side elevational view of a resistor constructed in accordance with the functional principles indicated in FIGURE 1;

FIGURE 3 is an elevational end view of the resistor shown in FIGURE 2;

FIGURE 4 is an elevational view of two snug-fitting ring segments employed as part of the bridging element to engage the two resistance wires;

FIGURE 5 is a similar view of FIGURE 4 with the rings shown engaging the two resistance wire elements to establish an electrical bridging connection between those wire elements;

FIGURE 6 is an end elevational view of the resistor shown in FIGURE 2;

FIGURE 7 is an elevational view of the micrometer end of the resistor taken with respect to FIGURE 6;

FIGURE 8 is a front elevational view of the fron wall of the carriage;

FIGURE 9 is a side view of the carriage; and

FIGURE 10 is an elevational view of the back wall of the carriage.

As shown in FIGURE 1, an adjustable resistor 10 is shown comprising two linearly disposed resistance elements 12 and 14, both engaged by a movable bridging device 15. The two resistance elements 12 and 14 are part of a single U-shaped wire, whose central bail section 11 is anchored in a :slot 13 in wall 32 of the supporting structure as in FIGS. 2 and 6. The bridging device 15 rides on a lead screw 18 which serves to axially and adjustably position the bridging device 15 to determine the length of the section of each of the two wire elements 12 and 14 to be included in the resistance circuit between two fixed terminals 20 and 22 which provide suitable connecting terminal points for connection to an external circuit 24-.

The two linear resistance elements 12 and 14 may be made of any material having suitable resistivity for the use to be made of the resistor. For simplicity of explanation, it will be considered that those two resistive elements 12 and 14 are of suitable alloys to provide the required range of resistance values desired within the limits of the small dimensions permitted for the resistor.

In a construction to which the present invention has been applied, to enable the resistor to be made as small as possible, for example as shown in FIGURE 2, the

length is as small as 1% inch and the diameter as small as /2 inch.

Returning again to FIGURE 1 for the functional showing, the wire element 12 is supported and held taut between the two end walls 32 and 34. The wire element 14 is also supported and held taut between the same two end walls 32 and 34. The two wire elements 12 and 14 are part of one wire member bent into a U- shape, as shown. The two wire elements 12 and 14 are disposed to be parallel to a central longitudinal axis 35 which is also the axis of the lead screw '18 for adjustably positioning the bridging member 15.

The lead screw 18 is shown supported between a front wall 36 and the rear end wall 34, shown to be part of the main structure of the switch. The lead screw 18 is supported between those two walls 36 and 34 for free rotation without translation. The front end of the lead screw is shown provided with a suitable slot 40 to receive the tip of a screw driver for adjustably turning the lead screw 18 to position the bridging member 15 as desired.

each other by two rigid tie and guide rods 82 and 84.

The supporting structure consisting of the two end walls 32. and 34 and the tie rods 82 and 84 is supported on, and anchored to, a front bracket 50. Secured to the bracket 5.0/is a hollow sleeve 54, externally threaded, which serves as a support, for disposition in a suitable supporting bracket or chassis wall, to support the entire switch 10. The threaded sleeve 54 and the bracket 50 and the end wall 32 of the supporting bracket for the wire elements 12' and 14, are locked together by a pin 56 as shown in FIGURE 7.

The externally threaded sleeve 54 serves essentially as a bearing support for the threaded lead screw 18. The lead'screw 18, itself, in turn, serves as a unitary support for the two resistance wires 12 and 14, the end walls 32 and 34, and the tie rods 82 and 84, and also serves as a support for the bridging member 15 which is arranged to be axially manipulated and shifted upon rotation of the lead screw 18. The two end walls 32 and 34, and bridging member 15 provide three-point support that prevents the tie rods 82 and 84 from skewing.

When the switch is assembled, as shown in FIGURE 2, with the locking pin 56 as indicated in FIGURE 7, the switch may be threaded into a wall 58 of a support or chassis upon which the switch is to be mounted. A cover 60, in FIGURE 2, is placed over-the switch to protect the elements against dirt or dust. Suitable openings 62 and 64 in the cover 60 permit the terminals and 22 at the ends, of the wires to extend through the cover'60, and be then sealed.

In order that the advantage of the linear disposition of the two wire elements 12 and 14 may be fully realized, a feature "of the present invention is to provide in the bridging member 15 an arrangement which permits the bridging member 15 to readily adapt itself to the two wires 12 and 14 without any external constraint on the bridging member 15 that would tend to vary the frictional contact resistance between the bridging member and the wires. As'shown in FIGURES 4'and 5, the functional elements of the bridge 15 consist of two ring segments 72 and 74', each consisting of a circular ring with, a part removed to provide a gap, and to leave the ring relatively resilient; The two rings 72 and 74 are disposed concentrically, and their respective radial dimensions are such that the inner ring segment 72 fits snugly within the outer ring segment 74. The dimensions are also so related to the spacing of the two wires 12 and 14 from the central axis of the switch, that the wires 12 and 14,will just rest-on the external peripheral edge surface of the inner ring7-2.

The two rings 72 and 74 are supported on andin the carriage 80 so they will be held against, relative displace ment, once they are assembled to engage the two wires 12 and 14, as in FIGURE 5. The action of the lead screw in moving the carriage 80 forward or backward on the wires 12 and 14'wou1d' have a turning torque tending to turn the carriage 80 around the central axis. In order 7 to prevent any such turning, so that the movement of the carriage 80 and the two rings 72 and 74 of the bridge 8, 9 and 10. As there shown, the carriage comprises a front wall 86 as in FIG. 8, and a rear wall 88, as in FIG. 10. The front wall 86 has an integral co-axial circular hub 87 to seat and support the inner ring 72 in selected angular position. The front wall 86 also has two sections removed to provide two spaces 92 and 94 through which the two wires 12 and 14 may extend and pass freely as the carriage 80 is moved back or forth along those wires.

The rear wall 88 of the carriage 80 is a flat circular plate, which is suitably cemented to the face 95 of the hub 87 after the two springs 72 and 74 are placed in position as in FIGURES 8 and 9.

The front wall 86 has a central concentric bore 100,

threaded to ride on lead screw 18, and two spaced guide holes 102 and 104 to enable the wall 86 to ride along on the two guide rods 82 and 84. The two cut-outs 92 and 94 permit the two wires 12 and 14 to extend through the carriage 80 as the carriage is adjustably shifted to move the bridging springs 72 and 74 along the two wires 12 and 14. i

The rear wall is provided with similar aligned holes, such as a central bore A- for lead screw 18, two guide holes 102A and 104A for guide rods 82 and 84, and two wires passage holes 106A and 108A for the two wires 12 and 14.

As shown in FIGURE 3, the slide rods 82 and 84 are supported at one end in the end wall 34. Similarly, the two wire ends of wire elements 12 and 14 are pulled taut by suitable terminal elements 20 and 22 on the outer end wall 34.

Thus, by means of the construction of the resistor with the wires arranged as shown as linear elements, with a bridging element subject to continuous movement in either direction, the amount of resistance included'between the terminals of the wire elements for connection to an external circuit may be controlled to an extremely fine degree of adjustment, depending upon the pitch of the lead screw 18.

By means of the loop or U-shaped arrangement of the resistive element with the bale of the loop anchored on one end wall element of the supporting structure, and the two sides of the wire loop extended as taut linear elements, the resistor arrangement provides a very simple construction with a bridging element that does not require connection to a terminal related to the external circuit.

Various modifications may be made in the details of construction and in the arrangement of the resistor without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is: 1. An adjustable variable resistor comprising an elongated structural frame having an axis, and consisting of two end plates co-axially disposed, and two parallel tie rods radially spaced from said axis and disposed parallel to said axis and disposed between and secured to said two end plates to holdsaid two end plates in fixed rigid spaced relationship; a wire loop in U-shape, with a bail and two side elements threaded through both end plates with the hail a bridging element transverse to said axis for engaging,

each of both wires'over a small continuous incremental length, said axially shifting bridging element including, two concentric circular ring segments, each having a gap to leave the shank of the segment resilient, one ring segment as an inner ring segment fitting and nesting in the other or outer ring segment with the two.

gaps disposed diametrically opposite each other and with the gap of the outer ring segment disposed within the lateral space between the two wires and in a plane transverse to said wires, and with the two wires disposed between the outer peripheral surface of the shank of the inner ring and the inner peripheral surface of the outer ring just adjacent the ends of the ring adjacent the gap;

a carriage for supporting the two ring segments in nested position and having a supporting plate for said ring segments, said supporting plate having a co-axial threaded bore;

means including a threaded lead screw co-axially supported between said two end plates, and threaded through said threaded bore of said carriage for axially moving said carriage to shift the position of said bridging ring elements on said wires;

and means for rotating said threaded lead screw to axially shift said carriage.

2. An adjustable variable resistor, as in claim 1, in

which References Cited by the Examiner UNITED STATES PATENTS Bachmann et a1 338-177 X Thompson 338-426 Green 338-177 X McCabe 338-97 Carson et a1 338*176 X Bourns et a1 33897 X FOREIGN PATENTS Great Britain. Great Britain.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner. 

1. AN ADJUSTABLE VARIABLE RESISTOR COMPRISING AN ELONGATED STRUCTURAL FRAME HAVING AN AXIS, AND CONSISTING OF TWO END PLATES CO-AXIALLY DISPOSED, AND TWO PARALLEL TIE RODS RADIALLY SPACED FROM SAID AXIS AND DISPOSED PARALLEL TO SAID AXIS AND DISPOSED BETWEEN AND SECURED TO SAID TWO END PLATES TO HOLD SAID TWO END PLATES IN FIXED RIGID SPACED RELATIONSHIP; A WIRE LOOP IN U-SHAPE, WITH A BAIL AND TWO SIDE ELEMENTS THREADED THROUGH BOTH END PLATES WITH THE BAIL OF THE LOOP PULLED AGAINST THE OUTER SIDE OF ONE END PLATE AND WITH THE TWO TERMINAL ENDS OF THE TWO SIDE ELEMENTS ANCHORED IN TENSION AT THE OUTER SIDE OF THE SECOND END PLATE, AND WITH THE TWO SIDE ELEMENTS DISPOSED PARALLEL TO SAID AXIS AND SYMMETRICALLY SPACED THEREFROM; A PAIR OF TERMINALS AT THE TERMINAL ENDS OF SAID TWO WIRES FOR CONNECTION TO AN EXTERNAL CIRCUIT; A BRIDGING ELEMENT TRANSVERSE TO SAID AXIS FOR ENGAGING EACH OF BOTH WIRES OVER A SMALL CONTINUOUS INCREMENTAL LENGTH, SAID AXIALLY SHIFTING BRIDGING ELEMENT INCLUDING TWO CONCENTRIC CIRCULAR RING SEGMENTS, EACH HAVING A GAP TO LEAVE THE SHANK OF THE SEGMENT RESILIENT, ONE RING SEGMENT AS AN INNER RING SEGMENT FITTING AND NESTING IN THE OTHER OR OUTER RING SEGMENT WITH THE TWO GAPS DISPOSED DIAMETRICALLY OPPOSITE EACH OTHER AND WITH THE GAP OF THE OUTER RING SEGMENT DISPOSED WITHIN THE LATERAL SPACE BETWEEN THE TWO WIRES AND IN A PLANE TRANSVERSE TO SAID WIRES, AND WITH THE TWO WIRES DISPOSED BETWEEN THE OUTER PERIPHERAL SURFACE OF THE SHANK OF THE INNER RING AND THE INNER PERIPHERAL SURFACE OF THE OUTER RING JUST ADJACENT THE ENDS OF THE RING ADJACENT THE GAP; A CARRIAGE FOR SUPPORTING THE TWO RING SEGMENTS IN NESTED POSITION AND HAVING A SUPPORTING PLATE FOR SAID RING SEGMENTS, SAID SUPPORTING PLATE HAVING A CO-AXIAL THREADED BORE; MEANS INCLUDING A THREADED LEAD SCREW CO-AXIALLY SUPPORTED BETWEEN SAID TWO END PLATES, AND THREADED THROUGH SAID THREADED BORE OF SAID CARRIAGE FOR AXIALLY MOVING SAID CARRIAGE TO SHIFT THE POSITION OF SAID BRIDGING RING ELEMENTS ON SAID WIRES; AND MEANS FOR ROTATING SAID THREADED LEAD SCREW TO AXIALLY SHIFT SAID CARRIAGE. 